Production of pulp and treatment of residual liquors, etc.



Dec. l1, 1934. L. BRADLEY ET AL 1,983,789

PRODUCTION 0F PULP AND TREATMENT OF RESIDUAL LIQUORS, ETC

Original Filed Jan, 25, 1928 URI/585K 1S/DUAL Lm /a .aan

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sogas "i 511461 TfR G' wATfR AML I C004 Solms/.f5 I' Patented 11, 1934 UNITED STATES vPATENT OFFICE PRODUCTION F PULP AND TREATMENT 0F BESIDUAL LIQUOBS. ETC.

Unn Bradley, Montclair McKeefe, New York, N. Meliecfe Corporation. poration of New York N. J., and Edward P. Y..I'lllmntoradley New York, N. Y., a cor- 21 claim. (ci. zs-izs) lhis invention relates to the treatment of alkali-metal compounds, particularly alkalimetal carbonates and sulfur-bearing compounds of alkali-metal.

This invention relates, more particularly, to improvements in the production of pulp and in the production of chemicals, vfor example from the residual liquors of a pulp making process for use in producing liquors for use in carrying out a pulp making process. 'I'he invention includes improvements in the cooking of wood, etc.

for the production of chemical pulp; in regenerative or cyclic methods of pulp production with regeneration of cooking liquors from residual liquors of the same or different related processes;

in new combinations of pulp making processes;

in the production of alkali-metal compounds; in the treatment of residual liquors for the production therefrom of alkali-metal compounds or of cooking liquors, etc.

The present invention includes a process for converting a sulde of an alkali-metal into a carbonate of an alkali-metal, e. g. sodium carbonate, in which the -sulilde is treated with a suitable acidic material such as available carbon dioxide in a non-gaseous form, and in which a volatile sulilde, e. g. hydrogen sulfide, is produced and removed.

The present invention also includes a process for the production of a sodium acid carbonate in a solid state, and a process in which solid sodium acid carbonate is utilized in the treatment of solutions containing sodium sulfide to form a carbonate of sodium and hydrogen sulfide.

The invention also includes a process of treating admixed sodium carbonate and sodium sulde, such, for example, as results from a strongly reducing furnace treatment of material derived from residual liquors from a pulp making process in which sodium-sulfur compounds are employed, for the production of liquors containing a sulnte of sodium, in which process the treatment of a solution of such sodium carbonate and sodium suliide is so conducted as to convert the sodium content of the sodium carbonate and the sodium sulfide largely into a sulte of sodium, and in which the formation of sodium thiosulfate is regulated or may even be substantially prevented.

The invention also includes cyclic or regenerative processes for producing pulp from wood, etc., as well as interrelated processes for producing pulp, in which, or in some of which processes, a'

digesting liquor is employed which includes a sulte of sodium, and in which the residual liquor is treated to regenerate or reform a digesting liquor for use in the same or a related process, particularly a digesting liquor which contains a sultlte of sodium, and which may or may not contain sodium thiosuliate in regulated lesser amount, e. g. less than the amount of the sulnte 0i sodium, and in which the resulting digesting liquor is employed for digesting wood, etc. for the production of pulp therefrom.

Ihe invention includes improvements in the production of liquors containing a considerable amount oi' a sulilte of sodium, with little if any, or with only regulated lesser amounts of, sodium thiosulfate, by utilizing the sodium content of liquors which contain considerable amounts of sodium'carbonate and of sodium sulfide.

The invention includes various improvements in the above and other processes, which will more fully appear from the following more detailed description.

The present application is a continuation in part yof our prior applications now matured to patent: Serial No. '104,176 nled April 4, 1924 (Patent 1,896,038); Serial No. 713,257 filed May 14, 1924 (Patent 1,898,613); Serial No. 133,289 filed Sept. 2, 1926 (Patent 1,795,754); Serial No. 133,- 290 filed Sept. 2, 1926 (Patent 1,870,944); and Serial No. 686,137 filed Jan. 14, 1924 (Patent 1,833,313).

When wood, etc. is cooked or digested with a cooking liquor containing sodium-oxy-sulfur compounds, such as a sulfite of sodium, and when the residual liquor from such cooking process is suitably concentrated and the resulting solid material heated in a calcining or/and smelting furnace to decompose sodium-organic compounds, etc., the sodium compounds are converted largely into sodium carbonate and sodium sulfid, particularly if the furnace operation is carried out under suitable reducing conditions toward and near the end of such furnacing treatment, e. g. by heating the sodium compounds to a temperature sufficient to melt them and in the presence of incandescent carbon in sumcient amount to insure the sodiumsulfur compounds in the furnace product being largely, if not entirely, in the form of sodium sulild. A concentrated aqueous solution of the sodium compounds present in such a furnace product will usually contain a large amount of sodium carbonate and oi' sodium sulfide and usually with the former being in larger amount than the latter.

'I'he present invention includes improvements in such processes in which such a solution containing sodium carbonate and sodium sulfide is produced. According to the present invention,

of some of the sodium content of the sodium carbonate and sodium sulilde into a sultlte of sodium. without the formation of large or prohibitive amounts of sodium thiosulfate during the treatment. such treatment may be a direct or an indirect treatment which may be considered an oxidizing treatment in the sense that sodium sulfide is converted at least in part into a sulnte of sodium. 'I'he present invention includes improvements in both indirect and direct treatment of such sodium sultld, as well as combined indirect and direct treatment of the nature of oxidation treatment for producing solutions containing a suliite of sodium either without or with regulated lesser amounts of sodium thiosulfate, sodium carbonate and sodium sulfide.

The present invention includes improvements` in the treatment of solutions including sodium carbonate and sodium sulde with carbon dioxide, and particularly with available carbon dioxide supplied to the sulfide of sodium in a non-gaseous form and advantageously and preferably in sumcient amount to convert most of the sodium sulde into a carbonate of sodium and to convert sulfur thereof into a volatile sulilde, with removal of volatile sulilde from a carbonate of sodium remaining with the liquor.

While, in its broader aspects, the invention includes improvements in the carbonating of solutions containing a soluble alkali metal sulde with carbon dioxide supplied to the solution in gaseous form, particularly in combination with other features of the process, the invention includes improvements broadly in the carbonating of such solutions with available carbon dioxide supplied to the alkali-metal suldde in a nongaseous form.

Thus the available carbon -dioxide may be supplied in the form of a suitable carbonate or bicarbonate or other form such that available carbon dioxide thereof will react with sodium sulfide during the process. A particularly advantageous means of supplying available carbon dioxide is a sodium acid carbonate, or other acid carbonates which give up some of their carbon dioxide contentso as to react with the sodium sulfide to form a carbonate oi sodium and to release sulfur of the sodium sulilde in the form of a volatile sulfide. A bicarbonate such as sodium bicarbonate is a particularly advantageous material to employ, and the invention includes an improved method of treating solutions including sodium suliide, with sodium bicarbonate to form sodium carbonate and to set free hydrogen sulfide. In referring to available carbon dioxide, we refer to the carbon dioxide content of such carbonate, etc. which is available to react with sodium sulfide to release sulfur therefrom and form a carbonate of sodium. Il'hus in sodium bicarbonate, NaHCOa, one half of its carbon dioxide content is considered to be available carbon dioxide. Other suitable acid carbonat of alkali metals can be employed.

In treating liquor including sodium carbonate and sodium sulfide with available carbon dioxide supplied in the form of a sodium acid carbonate. the liquor may be mixed with the required amount of the sodium acid carbonate, e. g. NaHCOa, which may advantageously be employed in the form of solid sodium bicarbonate, and the resulting admixture can then be agitated and subjected to reduced pressure or/and heated so as to remove hydrogen sulde which results from the in` ter-action between the available carbon dioxide such solutions may be treated for the conversion of the sodium acid carbonate and the sodium sulfide. The following assumed equations will serve to illustrate the reactions that may take place.

In using solid sodium acid carbonate it may advantageously be added in somewhat larger amounts than called for by these equations. e. up to twice as much. more or-less. especially wh it is desired to effect a substantially complete elimination of the sulfide sulfur from the solution as a volatile sulfide.

The present invention also includes an improvement in the production of sodium acid carbonate. e. g. sodium bicarbonate, which may be used in the treatment of such sodium sulde containing liquors, as well as an improvement in a combined process during part of which the sodium acid carbonate is produced, and during part of which the sodium acid carbonate so produced is employed for thus treating the sodium sulde-containing liquors. In its broader aspects, and particularly in connection with the part of the process in which the solid sodium acid carbonate is employed for treating the sodium carbonate-sodium sulilde liquors, the solid sodium acid carbonate may be obtained in any suitable manner, and by a method other than those included as part of the invention. The solid sodium acid carbonate can, however, be advantageously obtained by a regulated sulilting treatment of a suitably concentrated solution including sodium carbonate, preferably free or substantially free from sodium suliide and from sodium thiosulfate. By effecting a regulated sulilting of such a solution a solid sodium acid carbonate can be produced and the latter can be separated from the solution in solid form. The regulated sulting treatment is preferably conducted at a temperature below that at which sodium bicarbonate readily breaks up and releases carbon dioxide. The sodium carbonate material being sulilted is advantageously maintained at a temperature considerably below C. in order todeposit as much solid sodium acid carbonate as may be needed or is practicable. A solid carbonateof sodium may advantageously be present in the concentrated solution ,which is to be sulflted, so that the admixed solution and the solid carbonate of sodium form a slurry. When using such a slurry containing a solid carbonate ofsodium. a relatively large amount of-solid sodium acid carbonate can be `prepared by regulating the sul'- iiting step so as to convert the desired amount of soda into sodium sulte while keeping the materials cool enough to avoid objectionable decomposition of the sodium acid carbonate formed, and cool enough to deposit as fmuch of the sodium acid carbonate as a solid as can-be readily and practically done. bly below 60 C. are advantageously employed. e. g. between 5 and 50 C. The regulated sulilting step may be indicated by the following assumed equation, although not limited thereto.'-

The resulting sulnted liquor contains sodium sulilte in solution. This solution may be sep- Thus temperatures considera.-V

arated from thev solid sodium acid carbonate in any suitable and convenient manner and the sodium acid ,carbonate (preferabLv after suitably washing to remove sodium suliite) is then available for use for the treatment of the'sodium sultide containing solution to convert sodium sulfide into a carbonate ot sodium and to set i'ree sulfur of the sodium sulnde in the form of hydrogen sulfide.

In its broader aspects, the solution or liquor which is to be treated with the sodium acid carbonate (or with Iavailable carbon dioxide supplied in other suitable form), and which usually contains more sodium carbonate than sodium sulde, can be obtained from any suitable source and in any suitable manner. However, such liquor is advantageously obtained by -dissolving sodium compounds contained in a furnace product derived from residual liquor produced in the cooking or digesting of wood, etc., with cooking liquor which contains a sodium-oxy-sulfur compound, such as a suliite of sodium. Ordinarily and advantageously the liquor to be treated will have a greater amount of sodium present as sodium carbonate than as sodium sulde. However. it is an advantage to have a rather large amount of sodium sulfide present when the sulfur is t'o be removed as hydrogen sulde and such hydrogen sulfide is to be burned to form sulfur dioxide and the latter is to be employed for a sulntlng treatment, e. g. to convert a carbonate of sodium into a sulte of sodium, especially when the sullte of sodium isto be used as the principal reagent in the digestion or cooking of wood, etc., as herein described.

When wood is cooked or digested to produce chemical pulp with a cooking liquor including a y considerable amount of sodium sulflte, either alone or with moderate amounts of other chemicals, such as sodium hydroxide, sodium suld, sodium sulfate, sodium thiosulfate, sodium carbonate, sodium bisulfite, HiSOs, etc., and the residual liquor from the cooking or digesting operation is concentrated and the resulting dried product is calcined and/or smelted in the presence of incandescent carbon to convert the sodium compounds largely into the form of sodium carbonate, a considerable proportion of the soda in the furnace product is present as sodium sultide, particularly when the latter period of the furnacing operation is carried out under strongly reducing conditions. When the soda-containing furnace product or melt is leached vby' or dissolved in a small amount of water, the resulting solution will contain a large amount of sodium carbonate and sodium sulde. Such solutions, so obtained, which include sodium compounds derived from such residual liquor 'may be advantageously treated according to the present invention for the reproduction or regeneration of cooking liquor for use in the same process or a related process.

The sodium carbonate-sodium sulde liquor may require clarifying, before it is further treated, for instance when it contains carbon resulting from a strongly reducing furnace treatment' in which Oxy-sulfur compound or compounds of sodium are reduced by incandescent carbonaceous matter to form sodium sulfide. Such liquor may be clarified by ltering or otherwise, either before or after itstreatment with the available carbon dioxide and the removal of volatile sulfide formed. The liquor may'thus be treated with the available carbon dioxide to form a carbonate of sodium and a volatile sulfide, after which it is more suitably lterable through cotton fabric while hot and is less destructive upon such fabricbecause of the preliminary decomposition oi' the sodium sulde in the liquor.

The liquor, after' the carbonating and related treatment under 'conditions to remove substantially all or at least a maior portion of the sulnde-sultur as a volatile sulfide, may be cooled. ii' needed, by any suitable means down to a temperature which is suitable and advantageous for the regulated suliiting step in which solid sodium acid carbonate is formed and separated from the liquor. A heat interchanger may, ii desired, be employed so 'as to preheat sodium sulilte liquor with such a warm sodium carbonate containing. liquor. The sodium sulnte liquor remaining after the separation of solid sodium acid carbonate formed in the sultlng step may thus be v acid carbonate and to produce a liquor containing sodium sulte together with a small but regulated amount of a carbonate of sodium, which liquor can be advantageously employed as it is or modied to produce a cooking liquor for use in the cooking of wood, etc, in carrying out the cyclic or inter-related pulp lmaking process; and residual liquor from such a process can advantageously be treated in such a way as to produce a furnace product or melt from which a sclution of sodium carbonate and sodium sulfide may be obtained, and which may then be treated by the carbonating and' related steps of the process to remove sulde-sulfur and to produce a carbonate of sodium solution free or relatively free from sulde-sulfur, which solution may then be subjected to a regulated sulting treatment for the production of solid sodium acid carbonate and a solution containing sodium sulflte and some carbonate of sodium, which may be used in a further step or steps in carrying out the cyclc or inter-related process or processes.

Y The regenerated cooking or digesting liquor may be alkaline, neutral or acid to litmus when charged into the digester for the cooking operation. Such digesting liquors may contain substantially only normal sodium sullte (NazSOx) as the digesting agent, or they may comprise variable mixtures of normal sodium sulte and sodium acid sulflte, or they may in some cases contain only or mainly sodium acid sulte (NaHSOs) as the digesting agent, or they may contain both sodium acid sulfite and excess sul furous acid. Instead of containing some sodium acid sulilte, the digesting liquors may be either alkaline or neutral to litmus and may contain a suitable compound or compounds, in suitable proportions and amounts, such as sodium sulfte, sodium hydroxide, sodium thiosulfate, sodium sulfide, sodium sulfate, sodium carbonate, etc.

Where the cooking liquor contains sodium monosulte in suillcient amount it may also contain a lesser and regulated amount of sodium thiosulfate, as explained in our prior applications, Serial No. 704,176 and 713,257; and the present invention enables the amount oi sodium thiosulr fate present in such cooking liquors -to be regulated and controlled.

The present invention is particularly advantageous in cases wheresodium thiosulfate is not desired or permissible in the cooking liquor, or

v cooking liquors portion sulfate is to be present therein.` The processl of the present invention enables a maior part of the sulfide sulfur to bc'removed from the carbonated liquors, and enables the resulting liquors-to be suii'ited soas to facilitate producing therefrom cocking liquors containing a moderate amount of,

or substantially free lfrom sodium thiosulfate.

The process of the present invention is particularly advantageous for use in a cyclic or regenerative process in which strongly acid sodium suliite digesting liquors are employed. When the digestingliquors have a sufiicient quantity of sodium suliite, and the sodium sulflte is used in sufficient amount in proportion to the amount of the wood or other raw brous material digested, and when only a suitably regulated lesser amount of sodium thiosulfate is present, a superior result is obtained as compared to that obtained when the digesting liquor contains an excessive amount of sodium thiosulfate. This is true not only when the liquor is either neutral or alkaline to litmus, but it is particularly true when the digesting liquors are strongly acid to litmus at the time they are charged into the digesters in which the digesting or cooking operation takes place. In general, the larger the proportion of free or uncombined sulfur dioxide as compared with the combined sulfur dioxide (as sodium monosulflte) the greater the desirability of having the sodium sulnte in sufllcient excess over the thiosulfate, so

as to overcome the tendency of the latter to injure the quality of the fibrous material.

The present cyclic or regenerative process, in which sodium carbonate and sodium suliite-containing liquors are carbonated and the carbonate of sodium thereafter sulilted, enables regenerated cooking liquors to be produced and employed substantially free from sodium thiosulfate, or con taining only suitably limited and regulated amounts of sodium thiosulfate, and enables cooking liquors to be regenerated which are either neutral or alkaline to litmus, or which contain sodium bisulflte as well as sodium monosulilte and which maybe acid to litmus, as well as cooking liquors containing mostly sodium bisulflte or containing sodium bisulnte with an excess of sulfurous acid beyond the bisulfite stage.

The reactions which take place during the digestion of wood, etc., with such sulilte of sodium (whether neutral, alkaline or acid to litmus) are such that a maior portion of the sodium content of the residual liquor from the digesting treatment can be readily converted by evaporation, calcination and smelting, into a product consisting mainly of sodium 'carbonate and sodium sulfide; and a solution'of such sodium carbonate and sodium sulfide can then be treated by the carbonating, volatilizing and sulfiting treatments of the presentl invention for the regeneration of further amounts of suitable cooking liquors which include a sulilte'of sodium.

The cyclic or regenerative process is particularly applicable to the cooking ofwood to produce pulp therefrom, but in some 'of its broader aspects it is also applicable to the digesting or cooking of other cellulosic-fibre bearing materials which can be digested or cooked to render soluble a sufllcient of the non-fibrous organic materials` thereof so as to render fibres readily-separable from each other by mechanical treatment.

After the wood or othermaterial has been digested or cooked to a digesting liquor, e. g., containing a sulnte of sodium. thev resulting residual liquor may be sellassenso where only a small and limited amount of thiothe required extent by such ma from me fibrous mmm n un .residual llquoris acid to litmus, it may. if desired, be made either neutral or alkaline to litmus by adding a sumcient amount of a'suitable alkaline material thereto, e. g., a carbonate of or/and a sulfite of sodium, which may advantageously be some of the sodium carbonate and sodium sulnde which is obtained by the step or steps of the complete process of the cycle in which residual liquor is concentrated and sodium compounds are furnaced under .reducing conditions; Such addition of alkaline material, -in case such` material is added to residual liquor, may be made either before or after effecting a partial concentration of the residual liquor, either without or advantageously with some admixed washings. Ordinarily, however, such addition is made before concentrating such residual liquor although when it is desired to recover some sulfur dioxide from such a-,residualliquo the addition of alkaline material prior to such concentrating and recovery step may be advantageously dispensed with.

The residual liquor. after-removal of water therefrom, is converted into a solid material which is subsequently subjected to a furnacing treatment advantageously under reducing con-A ditions adapted to yield a furnace product containing sodium carbonate and sodium sulde in rather large amounts. By having a relatively large amount of sodium sulfide in the furnace product, a consider-able amount of a sulnte of sodium can be derived therefrom. by utilizing some of the sulfur'content thereof in a regulated oxidation of such sulfide sulfur. Hence, it is desirable to so arrange and conduct the digesting and fumacing treatments that a considerable amount of sulfur is present in the furnace product as sodium sulfide. The furnace product should preferably contain little if any thiosulfate, or polysulfide, and should contain mostly sodium Acarbonate and sodium sulfide, especially when thev indirect method of oxidizing the sulfide sulfur to sulilte is employed. To aid in providing a considerable amount of sodium sulfide in the furnace product, a considerable amount of a sulfate of sodium can be furnished to the solids resulting from the evaporation of the residual liquor, e. g. by adding it either before, or at the time, or after such solids are charged into the furnace.

When sulfate of sodium or acid sulfate of sodium is added to and mixed with the sodium bearing material at some suitable point or points priorl to completing the furnacing thereof in the 'reducing furnace.- the added sodium rsulfate will supply addedsodium and added sulfur to the process to make up for some of the losses or/and to provide a surplus of soda over that required for usein liquor employed in a sub-` sequent digesting operation. Additional carbonaceous material may, if necessary, be admixed with the furnace'charge'in which such sodium sulfate is included. the strongly reducing furnacing operation. such sodium sulfate is largely reduced to sodium sulfide. By supplying a relatively large amount of a sulfate of sodium in this manner, itis possible to produce a furnace product containing a large amount of sodium sultion, sodium carbonate or a sodium acid carbonate and sodium sulfite or an acid sulte can be produced. Considerable amounts of a carbonate of sodium (e.` g. sodium bicarbonate) can thus be produced for sale in conjunction with the` ploying sulfur dioxide, so produced,

production of liquors which contain a suliite of sodium and which are either free from or contain relatively small amounts of sodium thiosulfate. 'Die sulfur content of the sodium sulfate is also made available to a considerable extent as sodium sulfide which can be converted by subsequent treatment into a sulnte of sodium. e. g., by carbonating the sodium sulfide and driving oi! hydrogen sulfide. burning or oxidizing the hydrogen suliide to form sulfur dioxide, and emin a suifltim stepoftheprocesstoformasuliiteof sodium.

The hydrogen sulfide driven oi! during or subsequent to the carbonating treatment of the sodium sulfide may be burned to sulfur dloxide in a suitable combustion chamber. for example, a combustion chamber attached to and operated in conjunction with a sulfur burner,`and the resulting sulfur dioxide may be utilised in the sulilting step of the process and it may be supplemented by such additional sulfur dioxide as may be required therefor. It may be supplied. for example, by the burning of sulfur or suitable suliides. 'I'his burning of such hydrogen sulfide to form sulfur dioxide, and the utilisation of the resulting sulfur dioxide in the formation of a suliite of sodium is an indirect oxidation of the sulfurofthesodlumsulfide whichmaybeaccomplished without the formation of prohibitiveV amounts of sodium thiosulfate. By combining this indirect oxidation with the carbonate of sodium producing and utilizing steps of the process. an inter-related cyclic or indirect. process is provided of a particularly advantageous character. The sodium sulfide is decomposed by a sodium acid carbonate, and sodium carbonate.

and hydrogen sulfide are formed.` 'I'he hydrogen sulfide is removed and thereafter oxidized to form sulfur dioxide.- which is thereafter recombined with the sodium carbonate or other sodium compound in a direct or indirect manner to form a sulilte of sodium. In this way, the sulfur may be oxidized from sulde-sulfur to suliite-sulfur without formation of prohibitive amounts of thiosulfate.

'Ihe invention will be further described in connection with certain specific embodiments thereof. In the carbonating step lof the process, in which the sodium sulfide contained in the liquor is treated with available carbon dioxide in nongaseous form, diil'erent carbonating materials can be employed. The use of a sodium acid carbonate or sodium bicarbonate is particularly advantageous, a carbonate of ammonium can also be employed and has certain advantages. In some cases, carbon dioxide can be dissolved in water or in the liquor and employed in the form of a solution. These and other novel features of the process will be illustrated by the following more detailed description.

According to one embodiment of the invention. solid sodium bicarbonate is added. small portions at a time. to a concentrated solution containing sodium carbonate and sodium sulfide until the required amount of sodium bicarbonate has been added e. g. enough to convert the desired vamount of sodium sulfide into a carbonate of sodium. Th: solutions will generally contain more sodium carbonate than sodium sulfide, for example two molecular proportions of sodium carbonate to one, more cr less, of sodiumsulde. 'I'he amount of sodium bicarbonate added to such liquor is advantageously as much as. and preferably more than, called for by the assumed equation hereinbefore given for the conversion of all of the sodium sulfide into sodium carbonate with formation of hydrogen sulnde. The liquor may be treated advantageously below that temperature at which sodium bicarbonate or other acid carbonate present would bereadily decomposed so as to causev escape of any considerable amount of gaseous carbon dioxide from the liquor; that is, the temperature should be, for example, below 60 C., say between 5 and 50 C. 'I'he concentrated and relatively cool liquor and solid sodium bicarbonate are admixed and agitated together and hydrogen sulilde formed and released from the liquor is withdrawn from the vessel, for example by means of asuitable suction pump or fan capable of reducing the pressure within the vessel to a considerable extent (e. g. a reduction of 6 to 8 inches of mercury, more or less) to aid in the removal of hydrogen sulilde from the liquid. The vessel should be of such a character that the liquid can be agitated and the vessel subjected to a suitably reduced pressure. The amount of hy'- drogen sulfide retained by the liquor after such treatment is less when the amount of liquor is relatively small and the gas pressure above it is relatively low: accordingly, the use of a relatively small amount of concentrated liquor and the use of a relatively high partial vacuum are advantageous. vigorous agitation of such liquor also aids in removing hydrogen sulfide therefrom. With suitable temperature, vigorous agitation and low pressure, most, if not all, of the hydrogen sulfide can be readilyremoved, and the available carbon dioxide supplied. e. g. as sodium bicarbonate, can be utilized to good advantage.

It is possible. when the above treatment is of sufilcient duration and intensity to effect a substantially complete removal of hydrogen sulde, leaving little if any sulde-sulfur in the solution. However, if a substantially complete removal of sulfide sulfur therefrom is not necessary or is even undesirable, the carbonating and related operations can be regulated to leave part ofthe suli'ld-sulfur in the liquor. Ordinarily, and when a sulnte of sodium digesting liquor is to be produced, the greater part of the sulfide sulfur will be released and removed, and, in most cases, it-

will be more advantageous-,to remove all or nearly al1-of the sulfide sulfur, e."g. as hydrogen sulfide. The hydrogen sulnde, as pointed out above, may be burned in a combustion chamber connected to a sulfur burner and the resulting sulfur dioxide regained and'employed in the production of sodium sulte or an acid sulilte of sodium.

To aid further in the removal of hydrogen sulilde from the carbonated liquid, the liquid may be heated, for example after the major part of the hydrogen sulfide has been removed at moderate temperature. Such heating may be effected, for example, by a closed steam coil submerged in the liquid, and the liquid may be vigorously and continuously agitated either by mechanical means and/or a current of gases, such e. g. as carbon dioxide gases, passed through the liquid so as to expose a large surface thereof to the action of the gases.

In case the liquor which has been treated with a sodium acid carbonate still contains some sulilde sulfur, it may be treated with a suitable metallic compound, e. g., iron sulfate, so as to precipitate and remove the sulde sulfur as an insoluble sulfide; also, the treated liquor may be subjected to a regulated and suitable oxidizing treatment such-as -will oxldize to the desired extent any residual sulilde sulfur, elementary sulfur -or/and thiosulfate.

and thereafter the carbonate of sodium remaining with the liquor may be sulntedtothei'equireddegreeintheregulatedsuliiting treatment -which is subsequently carried out.

After sulilde sulfur. etc.. has been removed or disposed of by the procedure above described, the carbonate of sodium remaining with the liquor may be free from or substantially free fromsultur material such as will form or aid in forming an undesirable amount of sodium thiosulfate when the solution is subsequently sulted to produce sodium sulilte and solid sodium acid carbonate. i

Instead of using sodium bicarbonate in the car1 bonating step of the process, the availablecarbon dioxide may be supplied by other suitable carbonate which is capable of reacting with the sodium sulfide to form and release a volatile sulfide, such as hydrogen sulfide, etc. Thus, sodium compounds intermediate between the normal carbonate and bicarbonate may be used, as illustrated |`by the following equations, which illustrate the production of the bicarbonate and an intermediate carbonate as well as their reaction with sodium sulfide containing liquors.

In general, the smaller the volume of liquor employed for the carbonating treatment for a given amount of sodium sulfide the better and more readily the desired amount of volatile sulnde is eliminated. Accordingly, it is advantageous to `use a concentrated solution of sodium -carbonate and sodium sulfide in order to obtain better elimination of the desired amount of suliide sulfur. The employment of sodium acid carbonate in solid form avoids undesired dilution of the solution and, if the solution is sufliciently concentrated, gives a slurry containing solid sodium carbonate at the end of the carbonating treatment. Such slurry can advantageously be suliited and will give larger amounts of solid sodium acid carbonate upon the regulated sulflting, than when much more dilute solutions are employed.

Although it is desirable, in making optimum utilization of the available carbon dioxide supplied for the treatment of the sodium sulfide, to have the sodium carbonate-sodium sulfide liquor below C. when the liquor is treated with solid sodium acid carbonate, nevertheless a somewhat hotter'liquor can be employed in cases where some loss of carbon dioxide as gas is unobiectlonable, as where the available supply of solid sodium acid carbonate is much more than that required for forming and releasing the desired amount of volatile sulde. In such case, for example, the solid sodium acid carbonate can be placed in the bottom of a fairly tall tank and a somewhat hotter sodium carbonate-sodium sulde liquor poured on top of the solid sodium acid carbonate, care being exercised to insure that the liquor and the solids are well mixed beneath the surface of the liquor. The hydrogen sulfide released and removed may be delivered to the combustion chamber, e. g., of the sulfur burner.- Some carbon dioxide may be lost as gas in this modiiled method of operation, and in this case, a sufiicient excess of the sodium acid carbonate should be employed to allowl for such unutilised carbon dioxide.

Owing to the limited solubility of carbon dioxide in water or in aqueous solutions, an advantageous method to use when carbon dioxide is to be absorbed, e. g. from mixed gases containing it, is to produce a finely divided spray or atomintion of a liquor which is to be treated with the carbon dioxide. The carbon advantageously dissolved by the liquor while the gas is under pressure considerably greater than atmospheric. Ammonia may also be present in such gases. By spraying or atomizing such a liquor, e. g. a strong solution of sodium carbonate and sodium sulnde. into the carbon dioxide gases or into a mixture of gases which contains the carbon dioxide with or without ammonia, a very large amount of liquor surface is exposed to the gases and thus the absorption of the soluble gases is facilitated in an advantageous manner. If desired. the sprayed or atomlaed liquor and the gases (preferably under such increased pressure) can pass in opposite directions to each other, thus giving a counter-current effect. Enough available carbon dioxide should be supplied to the liquor to insure release and removal of the desired amount of sulild sulfur.

Either after or during the absorption of the carbon dioxide avolatile sulfide may be removed from the liquor and the sulfur content of the volatile suliide may be burned to produce sulfur dioxide. It is advisable to clarify the liquor before spraying or atomiaing it and bringing the sprayed or atomized material into contact with the carbon dioxide-bearing gases. Air orA other similar oxidizing gases are advantageously excluded from the gases while the volatile sulfide isbeing formed and releasedy and while it is being removed, in case it is desired to avoid or minlmize the formation of sodium thiosulfate in the liquor. y The carbon dioxide-bearing gases may b e introduced into a suitable chamber at ordinary pressure or with advantage at a pressure considerably above that of atmosphere and the liquor sprayed or atomized into the chamber which contains such gases at pressure above atmospheric, to take advantage of the increased solubility of carbon dioxide under such pressure conditions. After the required amount of carbon dioxide has been absorbed in the kliquor to convert the desired amount of sodium sulfide into a carbonate of sodium and to insure the elimiof the desired amount of suld-sulfur, it may be agitated and subjected to-.` reduced pressure or/and heat, e. g. by spraying the carbonated liquor into a chamber which is maintained at a reduced `pressure (e. g. below atmospheric pressure) by means of a suitable suction device or exhauster. And such liquor may be sprayed one or more times into such a chamber. The liquor may be heated, for instance, toward the end of its treatment in which a volatile sulde is being removed therefrom, to facilitate removal of gaseous material.

From the foregoing it will be understood that CO: gas is not passed through the sodium carbonate-sodium sultlde liquor, as in the former methods disclosed by other parties. but on the contrary the available 4carbon dioxide, Sn the desired amount, is supplied to the sodium sulfide in the liquor and thereafter a volatile suli'lde @is removed from such a carbonated liquor by means of reduced pressure or/and heat, and agitation may advantageously be employed to facilitate removal of the volatile sulfide. Some or dioxide is :,osagso -al1 of the resulting carbonate o! sodium can be thereafter suliited under conditions to remove carbon dioxide in concentrated condition and this carbon dioxide, alone or in conjunction with ammonia, canbe absorbed in liquor which containsa suliide of an alkali metal, e. g. sodium suliidel In casea more direct treatment is desired, the sodium carbonate-sodium suliide liquor may be boiled with enough lime to yield a liquor which contains a moderate amount of sodium hydroxide lin addition to the sodium suliide, together with a small or a moderate amount of sodium carbonate, and then the resulting liquor may be sepa.- rated from the solids. This treatment may serve also to clarify the liquor and to remove iron compounds if any in the liquor. Such causticiaed liquor may be further concentrated if desired or n.

When the sodium sulilde-containing solution is ilrst carbonated to release sulde sulfur which is removed therefrom in the form of a volatile sulilde, the carbonated solution so produced and remaining may be subjected to a regulated suliiting treatment for the production of a sodium acid carbonate and of a sulilte of sodium. The carbonate solution which is to be sulflted is advantageously a concentrated solution or a slurry containing an undissolved carbonate oi sodium, since the suliiting oi' such a solution or slurry results in the production oi' a solid sodium acid carbonate which can be separated from the liquor in considerable amount by filtration, centrifuging or otherwise.

In carrying out such a regulated sulflting treatment, heat is generated by the reaction and, unless provision is made for getting rid oi' a sumcient amount of this heat, the temperature of the liquor may rise to an objectionable point such that resulting sodium acid carbonate would be decomposed or/and an insumcient amount oi solid s odium acid carbonate would be precipitated. The suliiting is therefore advantageously carried out in a vessel provided with cooling means for removing a, desired amount of the thus generated heat. A cooling jacket or/and a lcooling coil, together* with agitation of the liquor and solids therein, can be employed for this purpose, this being particularly desirable when a concentrated sulfur dioxide gas is let into the liquor or sodium acid suliite is added thereto. By proper regulation and using proper cooling coils, etc., a proper temperature can be maintained.

If the carbonate of sodium liquor, remaining after the carbonating treatment and the removal of sulfide sulfur, is too hot or/'and too weak for the suliiting treatment, such liquor can be cooled or/and concentrated before such treatment. ItY can be concentrated, for example, in a. multiple effect evaporator to produce a suitably concentrated liquor such that upon subsequent cooling a considerable amount of a carbonate'of sodium will separate out as a solid. During. cooling oi such concentrated liquor, it may be suitably agitated to insure the separation of nely divided particles of a carbonate o! sodium, thus aiding in the subsequent treatment oi the resulting slurry with suliur dioxide or sodium acid sultlte. The unsulted. liquor can be cooled, if too hot, e. g. by showering the concentrated liquor into an open tower and causing a current of cold air with or without carbon dioxide gas to pass up through the tower in suicient amount to cool the liquor. The liquor can be recirculated one or more times ii desired, to effect further cooling. Such carbon dioxide as may be absorbed from the gases and retained by the liquor, in case a carbon dioxide bearing gas is utilized during the cooling treatment, aids in the production oi' a sodium acid carbonate.

The strongand cool carbonate of sodium material (which is advantageously a mixture of a solid-carbonate of sodium and a solution of a carbonate oi sodium (a slurry) especially when the subsequent production of a relatively large amount of solid sodium acid carbonate, e. g. NaHCOa is desired) is subjected to a regulated sulting operation, such as outlined above, by means of available sulfur dioxide supplied either as gaseous suli'ur dioxide or/and as an acid suly ilte of sodium, e. g. NaHSOz, in strong and cool solution, or as a solid, or as a slurry.

The material which is being sullted in the regulated sulilting step is maintained (by suitable means) cool enoughto retain all or at least most of the released or displaced carbon dioxide in the liquor or/and solids and to deposit an adequate amount of solid sodium acid carbonate for treatment of sodium sulfide. We have found that treatment of sodium sulde is facilitated, in the cyclic process of the present invention particularly, by keeping carbon dioxide, which is to be used to react upon sodium sulfide, in or with the liquor or liquors of the process or, e. g. in the form of a solid carbonate of sodium and by avoiding the release of such an objectionable or prohibitive amount of such carbon dioxide as a gas, at least by thus retaining or conserving such CO2 to such extent as is required for the proper and desired vtreatment of the sodium sulfide to form and insure the release and removal of the desired amount of a volatile suliide such as hydrogen lsuliide. Thus the material being rsuliited may be kept around a temperature of 10 to 30 C., more or less; although moderately higher temperatures maybe employed, especially when production of a relatively large amount of solid sodium acid carbonate is not required or desiredY In case suli'ur dioxide for the regulated sulting' step is supplied to the carbonate of sodium material in the form of a gas, e. g. such sulfur dioxide being derived from the combustion chamber in which hydrogen suliide released from sodium suli'lde is burned, such gas is advantageously cooled, ii' required, to a suitable point, e. g. 10 to 20 C., more or less, in a suitable manner and then brought into suitable contact with the carbonate of sodium material to be sulfited, e. g. a slurry o1' solid carbonate of sodium with a liquor such as referred to above. The desired amount of sulfur dioxide may be absorbed to form the desired amount of sodium sulte and of solid sodium acid carbonate, and the unabsorbed gases such as nitrogen, etc., which accompanied the sulfur dioxide gas from the combustion chamber, caused to pass on. Suchunabsorbed and cooled gases aid in maintaining the temperature of the sodium compounds at a suitable point, as some of the heat generated by the reaction when a. carbonate of sodium vis sulfited is transferred to such relatively cool and unabsorbed gases and thus removed from the material being sulted.

As stated above, the amount of carbonate of sodium sulted should be regulated so that the desired amount of solid sodium acid carbonate is separated out or otherwise obtained, and then such sulting should ordinarily be discontinued, although more solid sodium acid carbonate than is required. for the treatment of sodium sulde can be produced by suitably regulating the operations. The material being suliltsd is advantageously sufdciently cooled. by any suitable means, and suitably agitated while being suliited so as to obtain rather uniform treatment and avoid an over-sulnting of a portion of the carbonate of sodium material as a whole and an under-suliitlng of another portion, since an excessive n over-sulilting may cause an escape oi' gaseous carbon di` oxide to an undesired extent, a result which usually should be avoided in case eilicient and optimum use of carbon dioxide is sought. The following assumed equation may serve to illustrate the step when sulfur dioxide gas is used for regulated suliiting.

An alternative method of sumting the sodium carbonate material in a regulated manner is to carefully admix a concentrated and cool solution The acid sodium suli'lte can be obtained by absorbing eool sulfur dioxide gas, e. g..from the combustion chamber previously referred to above, in a regulated amount of concentrated and cool sodium sulilte solution. A slurry of solid sodium acid suliite in a solution of sodium acid sulfite, or solid sodium acid suliite alone, may be advantageously employed for the regulated sulilting of the carbonate of sodium material. especially when production of a relatively large amount of solid sodium acidearbonate is desired.

Whichever method of subjecting the carbonate of sodium material to the regulated sulflting treatment is employed, the solid sodium acid carbonate, e. g. NaHCOs, may be separated from liquor which contains sodium sulilts, and as much of the liquor as practical removed from the solids in any suitable manner. A suitable centrifuge or a filter-press or even a reduced-pressi'ire-illter of the rotary type may be employed when separating such liquor from such solids, and the solids may be treated to remove adhering llquorby any suitable method of washing, care being taken to avoid dissolving any excessive or prohibitive amount of` the solid sodium acid carbonate during any such washing treatment. Some of the excess solid sodium acid carbonate, e. g. some excess solid sodium acid carbonate which has previously been washed to substantially free it from sodium sulflte. may be employed to make a cold saturated solution oi' sodium acid carbonate, e. g. NaHCOa, and such solution may be used for washing another lot or batch of solid sodium acid carbonate to substantially free it from any objectionable amount, if any, of sodium sulfite adhering thereto.

is produced. Such liquor may be prepared in the manner outlined, so that it carries little if any sodium thiosulfate and the amount of the latter can be regulated and controlled by exercising due care.

The sodium sulfite liquor, separated from the sodium acid carbonate solid material produced by the regulated suliiting sten. may be clariiled in case this is needed or desirable. Should the sodium carbonate-sodium sulfide liquor, or a subsequent sodium carbonate containing liquor, contain an objectionable amount of iron-bearing material, e. g., as a ilnely divided iron carbonate or/and iron sulfid such liquor may be boiled with a small or moderate amount of quick-lime suilicient to aid inelarifying the liquor and removing iron-bearing material therefrom, and the rultixig liquor may thereafter be filtered or otherwise clarified in any suitable Such amount of caustic soda as may be be present in such a clariiled liquor, e. g. a illtrate, in ease it is to be carbonated thereafter by means of available carbon dioxide. should be allowed for and .an adequate amount of available carbon dioxide supplied in addition to and over that theoretically required to decompose the desired amount of sodium sulfide.

When an excess of solid sodium acid carbonate, egg. NaHCOs, or (NazCOaJNaHCOsHzO) the socalled sesqui-carbonate, is produced, i. e. more than is required for treating the sodium sulde to release sulnd sulfur and form a carbonate of sodium therefrom. the solid material may be d ivided into two parts, e. g. the smaller part or excess being used to make a saturated or concentrated solution of such sodium acid carbonate in cool water and this solution suitably employed for economically washing another and larger lot of solid sodium acid carbonate to remove adhering liquor in which sodium sulflte is present in the dissolved state. The resulting washings. carry-I ing some carbonate of sodium and some sulte of sodium, may be sulilted to produce either normal sodium sulilte or/and an acid ysulfite of The solid sodium acid carbonate may be substantially. or to the desired extent, freed from adheringliquor (which contains sodium sulflte) by washing such solid material, for instance, by displacement of such adhering liquor by means of cold water, or by means of a cold solution of sodium acid carbonate (advantageously a concentrated solution), or by means of a cold solution ofsodium carbonate (which may be a concentrated or a saturated solution), or by any other suitable means which will render and leave washed solid sodium acid carbonate, e. g. NaHCOs, substantially free from sodium sulte and provide a suii'icient amount of such washed solid sodium acid carbonate for the desired treatment of another lot of liquor which contains sodium sulde, such as the sodium carbonatesodium sulfide liquor referred to above. for example.

Such washing of the solid sodium acid carbonate to render it freeor substantially free from sodium sulfite is important when an eilort is being made Ato avoid the production of sodium thiosulfate or to minimize the amount of it produced, e. g. when treating a liquor containing sodium carbonate and sodium sulde by means of the solid sodium acid carbonate produced by a regulated sulilting treatment such as described.

When formation of a small or moderate amount sov of sodium thiosulfate in the liquor is not prohlbibonateneednotbe ascaretullywashedaswhen such thiosulfate formation is prohibitive or obiectionable, and in such cases (i. e. where a small or moderate amount ot such thiosulfate is less objectionable) the slurry oi' solid sodium acid carbonateand the liquor which contains the dissolvedsodiumsuliltecanusuallybescparatedsufilciently by means of a centrifuge or a good illterpres or a reduced-preasure-iilter of the rotary time. provided the solid sodium acid carbonate is not subjected to a pressure so low or/and to such a high temperature as will decompose it and cause the escape of an objectionable or prohibitive amount of carbon dioxide as gas. Solid sodium bicarbonate is apparently more stable under reduced pressure than imder high temperatures, however, so a reasonable and considerable reductioninpressuremaybeemployedto aidin separating the liquor from the solids.

Some of the sodium sulnte liquor produced by the regulated sulilting step. for example. may be kept cool and be employed (e. g. in a concentrated solution) to absorb S: gas to form an acid suliite. e. s. NaHSOi. and this acid sultlte of sodium may be employed for a regulated sulilting treatment of a concentrated and cool sodium carbonate liquor or slurry to form solid sodium acid carbonate and leave sodium sulte inthe solution. Such suliite o! sodium as is not used in connection with such sulfiting treatment of a carbonate of sodium can be utilized in any suitable manner, for example it may be used in the production of a digesting liquor for digesting wood. 'I'he sodium acid suliite employed for the regulated sulilting treatment, in case this method of suliiting is employed, may be in the form of a cold concentrated liquor or it may beinthe formofasolidorofamixtureof liquor and solid, the higher concentrations permitting of the production of relatively larger amounts of solid sodium acid carbonate.

Where more sodium acid carbonate or/and sodium carbonate is than is required either for treating sodium suliide or for forming a sulite of sodium, e. g. (NazSOg), either compound, i. e. carbonate or acid carbonate, may be disposed of as may be advantageous to such extent as it may be available therefor. Thus washed and dried sodium bicarbonate, which may be provided of a rather high purity by a method outlined herein, may be produced and sold to such an extent that it is not needed in a subsequent operation of the process or methods.

In the treatment of a concentrated liquor which contains sodium carbonate and sodium sulfide, we have found it desirable, in some cir-' cumstances, to charge the concentrated liquor and admixed solid sodium acid carbonate (which has been added for the purpose stated) into a de-salting evaporator, e. g. a single-eilect vacuum-pan heated by suitable means such as steamheating piping, and connected to suitable cooling pressure-reducing devices such as a condenser and a suction-pump. By means of such equipment, the liquor can be heated and subjected to a reduced pressure at the same time, thus aiding in the removal of a volatile sulilde (e. g. hydrogen sulilde), and while the hydrogen sulilde is being removed the carbonate of sodium liquor may be undergoing concentration, and this concentration may be regulated so that a considerable amount of a solid carbonate of sodium may be deposited in the de-salter; and this solid carbonate of sodium may, if desired, sepaproduced in the operations.

rated from the residual or mother liquor in any suitable manner. Ihe mother liquor. e. g. after such separation. may be sulnted in a regulated manner to produce a sulilte oi' sodium in solution and deposit a solid sodium acid carbonate. or the mother liquor together with all or a portion oi the solid carbonate oi' sodium thrown down in the de-salting evaporator may be subiected to the regulated suliiting step of the process. Such hydrogen sulilde as is removed from the de-salti'ig evaporator and is not condensed. may be conducted to the combustion chamber of a sulfur burner and therein burned to form sulfur dioxide, e. g. after condensing some of the water vapor therewith.

Sulfur canv be removed as a volatile sulde, e. g. hydrogen sulilde, and a carbonate of sodium removed as a solid in the de-salter, in a continuous type of operation. Thus the sodium carbonate and sodium sulilde and the solid sodium acid carbonate may be ied into the de-salting evaporator in a continuous manner, and hydrosen suliide and a solid carbonate of sodium removed more or less continuously therefrom. The mother liquor may build up in salts, e. g. sodium sulfate, and when the mother liquor has reached such a composition that it is advantageous to remove it from the de-salting evaporator, it may be removed and, for example, instead of suliiting such m'other liquor, it may in some cases be added to a residual liquor from a digesting step or steps of the process and sent to a furnace or furnaces to be so treated as to reduce sodium sulfate and form sodium sulilde thereby. Such mother liquor as is removed from the solid carbonate of sodium taken out of the de-salter, for instance by a centrifuge or bya lter, may be added to such other mother liquor as may be removed from the de-salting evaporator from time to time.

Solid carbonate of sodium removed from the de-salter may be disposed of in any suitable manner. Any surplus may be sold, or such carbonate oi' sodium may be subjected to a regulated sulflting step to form a sulfite of sodium in part and a solid acid carbonate of sodium in part. The suliite of sodium liquor produced in this manner, that is by obtaining a relatively pure carbonate of sodium in a solid state, separating it from mother liquor, and then sulfiting such carbonate of sodium in the presence of water,

is less liable to be contaminated with sodium thiosulfate than when mother liquor containing suliide-sulfur is sulilted: this being especially true when the de-Salted carbonate of sodium is carefully washed by cold water or by a cold and concentrated or saturated solution of sodium carbonate prior to such de-salted carbonate of sodium being sulted.

Having thus described in detail novel features of the process applicable to treatment oi' solutions produced by means of a step or steps of a regeneration process to produce cooking liquors for use in carrying out a pulp making process, we will now describe somewhat more in detail certain pulp making processes which are included in the novel cyclic or regenerative process. Certain of these pulp making processes in themselves as well as certain liquor treatment processes possess features of' patentable novelty and are claimed herein. y

In case the digesting treatment, e. g. of wood to produce chemical pulp, is carried out with an acid sodium sulnte liquor containing a large proportion of free sulfur dioxide, and in case some sulfur dioxide gas is relieved from the digester during the cooking operation. or from the liquor or digester at the end of or subsequent tothe cooking operation, thisnrelieved sulfur dioxide may be cooled and employed for a regulated sulsome sodium thiosulfate, together with a rather large amount of sulte as the main cooking reagent, the hydrogen ion concentration in the liquors appears to influence the tendency of loosely combined sulfur of the thiosulfate (l. e. one of the atoms of sulfur in sodium thiosuli'ate) to react with organic matter of wood or other cellulosic fibrous material, or of the liquor, with resulting production of darkened brous material which is unsuitable for some usages. Such darkened material is commercially unbleachable, in many cases. However, we have found that a small or moderate amount of sodium thiosulfate may be suitably employed inl such regenerated cooking liquors, provided the hydrogen ion concentration therein is kept away from such a point or points as would favor an undesirable reaction of loosely combined sulfur of the sodium thiosulfate upon organic matter present.

An advantageous method of overcoming or counteracting the tendency of such loosely combined sulfur to produce such unsatisfactory flbrous material, is to employ in the liquor an amount of sodium sulte (NazSOa) in' proportion to the weight of the raw brous material and of the non-fibrous organic matter therewith which is sufllciently large to prevent loosely combined sulfur being released from the thiosulfate and combining with organic matter to an objectionable degree, e. g. employing around 20%fto.40%, more or less, of NazSOa, based on the oven-dry weight of the wood. The sodium sulflte appears to exert a restraining or counteracting inuence on such undesirable sulfur reactions and such restraining or counteracting influence is of practical commercial value when such sodium sulte is present in adequate amount. A sutablylimited and regulated amount of free or uncombined sulfur dioxide (i. e. that SO: in excess of :the amount theoretically required to form NaaSO's with the available and reactive'sodium) may be employed, to facilitate the cooking operation, but an excessive or prohibitive amount of such free sulfur dioxide should be avoided, when thlosulfate is present, owing to its tendency to promote release of the loosely combined sulfur. q

A cooking liquor containing sodium thiosul fate in regulated amount and considerably less in amount than the sodium suli'ite present, which contains at least one molecule of sodium sulflte (NazSOs) for each molecule of sodium acid sulfite (NaI-i503)y has been found to be very useful in conjunction with the cyclic or regenerative process of the present invention, especially for cooking short-flbred woods` to `produce strong chemical pulp; and liquors ranging from equal molecules of sodium suli'lte (NaSOa) and bisuliite (NaHSOa) to liquors whilfi G01!- tain NazSOs and little or no NaHSOa, may be successfully used when they contain such a regulated and lesser amount of Isodium thiosulfate. Just what function sodium thiosulfate has in such liquors is not clear, but it is lmown to possess reducing properties and, therefore, whatever advantage such an amount of sodium thiosulfate' possesses is available in such regenerated cooking liquors. g Sodium thiosulfate present in the resulting residual liquor is advantageous in a subsequent step as it can supply soda and sulfur to form NazS.

We give below certain examples illustrating the cooking of wood with certain and particular cooking liquors which may be advantageously employed in the cyclic or regenerative process of the present invention.

10,000 pounds of wood chips, e. g. of poplar wood or gum wood (oven-dry basis) may be digested by means of either one of the following liquors, using about 40,000 to 50,000 pounds, more or less, of suchliquor. For example, the liquor may contain around 2,000 vto 2,500 pounds of available or reactive sulfur dioxide, more or less. of which around 1,000 to 1,250 pounds, more or less, may be present as sodium sulilte (NazSOa) and around 1,000 to 1,250 pounds, more or less, as sodium bisulfite (NaHSOs), and such liquor may also contain around to 250 pounds, more or less, of sodium thiosulfate (NazSzOzm or the liquor may contain around 2,000-to 2,500 pounds, more or less, of such sulfur dioxide of which around 1,250 to 1,500 pounds, more or less, may be present as sodium sulfite (NazSOa) and around '750 to 1,000 pounds, more or less, as sodium bisulte (NaHSOa), and such liquor may also contain around 200 to 500 pounds, more or less, of sodium thiosulfate (NazSzOs). Other similar liquors, e. g. containing more sodium as sulflte (NazSOs) than as bisulte (NaI-1803), may be Y employed, in each case having present in the liquor a considerable amount of available or reactive sulfite Ain excess of thatactually required for the digesting reactions.

Y By keeping the amount of acid in the liquorA down to a low point, as above shown, necessity for relieving sulfur dioxide gas from the digester during the cooking operation may be avoided -or minimized so that recovery of sulfur dioxide from e.

digester-relief gases -is rendered unnecessary. Such mildly acid cooking liquor may be advantageously heatedl to a temperatureconsiderably higher than is ordinarily used in the usual socalled acid-sulte process, e. g. to a temperature around 16o-180 C., more or less, and, owing to the relatively low acidity of the' cookingliquor, strong and rm pulps and high yields may be obtained in relatively short time. This type of cooking liquor and cooking operation makes fea- A.

sible the production of chemical pulps in` good yield and of excellent quality from deciduous woods, as well as from non-deciduous woods.

Moderately resinous pine wood, such as, e. g. jack pine, may be cooked by such liquors and good pulp produced, with little if any objection arising due to theresinous or pitchy content of such.

wood.

' In case the cooking liquor contains considerably more sodium present as bisulflte (NaHSOa) than is present as normal sulfite (NarSOa), it is desirable to conduct the process (and particularly the regeneration steps) in such a manner that the cooking liquor is substantially free from, or contains at the most only a relatively small amount of sodium thiosulfate; and when either sodium bisulte (NaHSOz) alone, or together with free sulfurous acid (H1803) is relied upon in the cooking liquor. it should preferably be almost, if not entirely, free from sodium thiosulfate.

When the cooking liquors contain a relatively large amount of free sulfur dioxide, the residual liquor from the digesting treatment of raw iibrous material therewith may be separated from the resulting fibrous material, then treated to remove water (and before removal'of water therefrom the liquor may be neutralized or made alkaline to litmus, e. g. as hereinbefore described) and the solids, including carbonaceous matter, fumaced in a suitable furnace under conditions adapted to form mostly sodium carbonate and sodium sulde from the sodium compounds in the concentrated material. 'lhe resulting sodium carbonate and sodium sulilde can then be dissolved in water, e. g. to make a concentrated liquor, this sodium sulfide subjected to a regulated oxidation treatment (e. g. by forming a carbonate of sodium and a volatile sulfide, removing a volatile sulfide and oxidizing it to form sulfur dioxide and later combining such sulfur dioxide with a carbonate of sodium) and with such precautions as needed to avoid the formation of more than a relatively small amount, at the most, of

sodium thiosulfate, and with such further suliiting as needed so as to regenerate a sulflte of sodium cooking liquor of proper composition and strength, and this regenerated sulnte of sodium cooking liquor may thereafter be employed for a digestion of wood or other raw fibrous material for which it may be suited. Alternately. material which contains sodium sulfide or/and sodium thiosulfate (e. g. also containing an adequate and suitable amount of caustic soda) may be oxidized by means of gaseous oxygen, for instance, by spraying concentrated liquor containing such a sodium compound into air which has been heated to a suitable temperature.

When the cooking liquors employed have a relatively large amount of sodium sulte (NazSOa), e. g. one having two or more molecules of NazSOa for each molecule of NaHSO3, it is advantageous to employ a relatively high cooking temperature. Thus good chips and such a cooking liquor may be charged into a digester, steam introduced into the lower portion of the digester in a manner to promote circulation of the cooking liquor therein, and with fairly uniform heating of the liquor through a period of, for example, around three hours, more or less, until a temperature of the cooking liquor of around l60185 C., more or less, has been reached. 'I'he liquor and brous material may be maintained approximately at such a relatively high temperature until the digestion has been carried to the desired degree. This may require a further period of around three to ten hours, more or less, relatively short periods usually being suitable for deciduous woods, while coniferous woods such as pines usually require a longer period than three hours for adequate digestion to produce chemical pulp suitable for bleaching.

Cooking liquors which are nearly neutral, or are mildly alkaline (to litmus), usually are milder in their action at a given temperature than those which have more acid (S01) and hence the milder liquors should be given sufcient heating both as to temperature and time in order to produce the' desired result. That is to say, with the milder liquors it is an advantage to employ tcmperatures higher than those temperatures which are usually suitable for use with liquors of relatively high acidity, i. e. containing relatively large amounts of uncombined or free sulfur dioxide and relatively small amounts of combined 80a. With relatively mild liquors, e. g. those which have as much soda in the form of NazSO; as of NaHBOJ, and which mild liquors include the range all the way down in acidity to liquors which contain nearly all of the SO2 as NaaSO: and have only a small amount kof NaHSO; present therein, a great variety of woods may be digested to 'produce chemical pulps of such relatively high quality that they may be employed in relatively large proportions to produce papers of good quality.

Such mildly acid liquors are particularly suitable ior the digestion of short-tlbred woods (such as gums, poplars, birches, maples, etc.) to produce quality pulps. Such mild liquors are also well adapted to the digestion of some moderately resinous pines, which usually are unsuited for pulping with the conventional so-called acid-sulfite process employing a high free sulfur dioxide together with a calcium base. owing to their resin or pitch content. Such mildly acid sulte of sodium liquors may, if desired, contain small to moderate amounts of sodium thiosulfate, but the amount of such thiosulfate should be kept below that which is liable to produce a darkened stock such as is commercially unbleachable. In general, the greater the percentage of SO2 as compared to sodium sulilte in such acid liquors, the lower the amount of thiosuifate which can be employed in such liquors.

The residual liquors from such digestion operations with such mild sulte-bearing liquors may be treated by processes of the present invention so as to regenerate digesting liquors of the same kind or of a different kind. Likewise, residual liquors from digestion operations with liquors which contain a relatively high proportion of free or uncombined sulfur dioxide may be treated by processes of the present invention to regenerate digesting liquors of the same kind or of a diierent kind; and sulfur thereof can be regained and used in the form of sodium sulfide as pointed out herein.

Residual liquor from a digesting operation in which the principal digesting reagent is a sullite, either with or without previous concentration, and either with or without having had alkaine compounds (e. g. sodium compounds) added thereto, may be (for example) introduced into the upper portion of a suitable scrubbing tower and subjected therein to the action of a current of gases derived from a furnace in which the reducing furnace treatment is conducted, the liquor owing over checker-work in the tower from top to bottom and the gases ascending through the checker-work. When such gases are suillciently hot, and when they carry some sodium compounds, the liquor may become more concentrated in sodium compounds during its descent through the tower; and if the gases carry some available sulfur trioxide, e. g. as sulfuric acid or as sodium sulfate, such liquor usually absorbs some of it. When such gases carry a large amount ofan uncombined acid which is capable of displacing sulfur dioxide from sodium sulfite, the gases beyond such scrubbing tower may carry a considerable amount of sulfur dioxide, escia-ily when the residual liquor charged into the upper portion of such a tower is acid to litmus and contains a considerable amount of an acid sufite of sodium.

When such efliuent gases from such scrubbing tower or chamber are scrubbed with a carbonate Vll',

' through af boiler, then through a spray chamber- -twith or wlthoutan electrical precipitator). then suitable hot gases (for example hot gases derived from the reducing furnace and after oxidation to form sulfur dioxide, and just after such hot gases have been passed through a steam boiler) while such gases are passing through a suitable spray chamber, the spraying or atomizing being carried out under such conditions that a considerable amount or substantially all of the water content of the sprayed or atomized material is removed by evaporation and sothat a highly concentrated liquor or a dry powdered material, as the case may be, is produced thereby.

Such spraying or atomizing may be in one operation, or the liquor may first be sprayed into hot gases to produce a concentrated liquor' and the latter thereafter sprayed or atomized into such hot gases and converted into a powdered vsodium-organicproduct. When producing such powdered material," the gases may be passed through an electrical -precipitator, which may be placed beyond the spray chamber. if desired, to collect suchdried material as may not have previously settled out from thegases. A scrubbing tower or chamber may be operated beyond such electrical precipitator and, for example, may be fed with a carbonate of sodium liquor so as to absorb sulfur dioxide, etc. from the gases when present therein.

When an acid residual liquor is sprayed or atomized in the manner disclosed, the gases beyond the spray chamber or/and electrical precipitator may carry a relatively large amount of sulfur dioxide which can be regained as pointed out.

In the treatment of thesprayed or .atomized residual liquor by means-of hot furnace gases, care should be taken to avoid over-heating and consequent carbonizlation'` of an undesired or objeetionable amount yof sodium-organic material derived from the digesting operation, especially when the resulting powdered sodium-organic material is to be used as fuel, e. g. as powdered fuelin the furnace, and the furnacing operation is to be carried out underv such reducing conditions that a relativelyf'large amount of sodium A'sulfide is to bev obtained in the furnacefproduct,

especiallyvwhen the hot productsof combustion of such powdered fuel are to be used a boiler 4for the production of steam.

When such hot products of combustion are passed through a boiler, some solids may be thereby collected; and these may be added to the concentrated liquor or t'o thepowdered carbonaceous materialwhich is to beburned inthe furnace.l

Thearrangement maybe such that the furnace gases-pass-through a combustion chamber, then through a scrubber, Aanni then tov atmosphere. Each of these devices may. have one or more sections either in parallel or in series, as may be desirable, and one or more suitable liquors may bev used in the spray chambers, towers, etc. Elec` trical precipitators may be employed with or may be placed Aafter a spray chamber or chambers so as to collect either solids or liquids or both. By evaporating substantially all of the water of the residual liquor by means of hot gases acting upon sprayed or atomized liquorv beyond the boiler,

thus getting a dry fuel, and using` this dry fuel and combustibles in the residue may be thereafter burned, e. g. under reducing conditions toform NazS.

By burning substantially dry sodium-bearing organic material in the reducing furnace, instead of using a concentrated liquor in the furnace, the hot products of combustion beyond the combustion chamber have a relatively greater amount of available heat, and such available heat can be utilized to advantage in producing steam in the boiler, owing to the relatively high flame-temperatures and to the relatively smaller amount of highly heated water vapor in such products of combustion. The furnacing operation may be advantageously so conducted thatl the sodium compounds derived from residual liquor, to a large extent, are deposited in the lower regions of the furnace, together with suilicient incandescent carbon to insure any sodium-oxy-sulfur compounds present being reduced to the desired degree and extent, i. e. so that a relatively large amount of NazS is formed together with sodium carbonate. f

. Sulfur dioxide, if any, contained in the relatively cool gases after they have passed beyond the spray evaporator or/and driers, and beyond the relatively hot scrubbing tower or towers, if any are employed, can with advantage'be regained by scrubbing such gases with a cool sodium sulflte liquor (to form an acid sodium sulflte liquor which can be used, e. g. for cooking raw 'sulte directly. Thus solid sodium carbonate,

in whole or in part, or/and mother liquor. present .after concentrating and cooling a substantially sulfide-free sodium carbonate'liquor, may be employed for recovering sulfur dioxide from furnace gases. e. g. those beyond the spray chambers vor/and relatively hot scrubbing towers in which residual liquor or liquors are treated by the furnace gases, preferably such as carry sulfur dioxide; Such sulfur-dioxide bearing gases may be derived, at leastin part, by burning combustible gases, under regulated oxidizing conditions, derived from a furnace in which sodium-organic materials,` from residual liquor resulting from cooking wood with an NaOH-Naas liquor, are calvcined or/and carbon burned. Sodium carbonate and vsodium sulde resulting from the reducing furnace treatment, e. g. in the form ofa `melt or smelt, may be dissolved in water in a lsuitable tank or dissolver provided with an agitatorand with a suitable coll of iron piping. and a cool neutral or alkaline sodium l sulnte liquor may be passed inside of this piping so as to obtain a preheating of such sodium sultite-liquor by absorbing heat from the hot sodium carbonate-sodiuml sulfide liquor in the tank or dissolver. In case it is desired to cool the latter liquor to down below 60 C., for example, cool water or other cool liquid in adequate amount and oi sumclently low temperature may be passed through this piping to effect the desired degree of cooling oi' the liquor in the dissolver.

'l'he processes of the present invention make feasible the operation of a pulp-mill or pulp-mills with one type of digesting liquor alone (employing a suliite of sodiumf therein) or with more than one type of digesting liquor; that is, it may be a single-liquor mili or a ."multlple-liquor mill. For example, a digestion of wood may be eifected by means of a cooking liquor which contains mostly sodium sulilte (NazBOi) as the digesting reagent, and with but little or no sodium thiosulfate present in such digesting liquor. The resulting residual` liquor may be separated from the resulting iibrous material, then suitably cooled, and enough sulfur dioxide absorbed therein or/and sodium bisulilte added thereto to produce a moderately acid cooking liquor which contains the desired amounts of free and of combined SO2, and this acid cooking liquor then employed tor a digestion of wood (etc.) The excess sodium sulte (NazSOg), i. e. that which was not consumed in the rst digestion treatment, remaining in the iirst residual liquor serves to supply soda and combined sulfur dioxide for the acid sodium sulilte cooking liquor made in this manner. Then an acid sodium sulte cooking liquor digestion (e. g. of wood) is carried out, the second resulting residual liquor separated from the resulting fibrous matter, and such latter residual liquor (together with wash waters if desired and with or without addition of alkaline material thereto) subjected to a concentrating treatment and the solids thereafter furnaced under strongly reducing conditions adapted to form mostly sodium carbonate and a relatively large amount of sodium suliide from the sodium compounds. These two compounds (NazCOa and NanS) are dissolved in water to form aliquor, this liquoris causticized to form an alkaline digesting liquor which contains caustic soda (advantageously in preponderating amount) and sodium sulde as its sole or as its principal digesting reagents.- and such alkaline cooking liquor is employed to'digest wood, etc., e. g. to form chemical pulp, and to form an alkaline sulfur-bearing. residual liquor. The latter residual liquor may then be concentrated and thesolids furnaced to convert most of the sodium compounds into sodium carbonate,

, the latter being either free from or accompanied by but a small amount of sodium suliide. These two materials may then be subjected to a regulated and controlled oxidation treatment, either direct or indirect or both, in accordance with the processes outlined in this specication, and the soda treated to form a sulflte of sodium cooking liquor which may either be free from free sulfur dioxide or contain such an amount thereof as will render the resulting liquor suitable for the digestion of wood to produce chemical pulp thereby. thiosulfate will be present in only small quantity, ii any, in such sulte of sodium cooking liquor. Such an operation is for a three-or-more-liquors mill.

An alternativemethod of operating, in a twoliquor mill, for example, is to carry out a digestion treatment on wood (or other suitable cellulosic-flbrous material) by means of a suitable cooking liquor which contains a sulte of sodium (such cooking liquor may or may not contain some normal sodium sulflte; and it may or may not contain some sodium bisuliite; and it may or may not contain any additional sulfur dioxide beyond the sodium bisulte stage) until such raw material is digested to the desired degree, e. g. until chemical pulp is obtained. The resulting residual liquor may thereafter be concentrated either with or without rendering it neutral or alkaline (e. g. by adding alkaline soda. material thereto, such as a mixture of sodium carbonate and sodium 'sulfide derived from a reducing furnace treatment of solids from a suitable residual liquor) and the solids furnaced under strongly reducing conditions to form sodium carbonate and a relatively large amount of sodium suliide, these compounds thereafter being dissolved and sodium carbonate in the resulting liquor causticized by means of lime to form a cooking liquor containing caustic soda (e. g. in Apreponderating amount) and sodium sulfide.

Such latter cooking liquor is then employed for a digestion treatment to produce pulpy matelrialfrom wood, etc. (e. g. chemical pulp) and the'resulting residual liquor treated by a process or processes of the present invention to eliminate organic matter and to produce a sulfite of sodium cooking liquor suitable for` digesting wood to produce chemical pulp (and with a regulated amount of thiosulfate or free therefrom) and the latter liquor then employed for such a. digestion treatment.A The reproduced digesting liquor may be an acid suliite of sodium liquor such as was first employed or it may be of a diil'erent composition so long as it is suitable for the operation to which it is to be put. In such a two-liquor mill operation, the amount of thiosulfate in the sulte-type of cooking liquor can be kept very lowl or absent.

In such a two-liquor mill operation sulfur is employed in a sulfite of sodium cooking liquor, then some oi the same sulfur is used in a liquor which contains sodium sulfide and some of the sulfur may then be regained and reused in the reformed or regenerated digesting liquor which contains a suliite .of sodium. Some of the same sodium is employed in each of the two digesting liquors. A-y sulfate of sodium may be employed for replacingV lost soda and some of the sulfur losses in the operations; or a. carbonate of sodium or sodium hydroxide may be employed to replace lost soda; or a sulfateof sodium and a carbonate of sodium or/and sodium hydroxide may be employed to replace some material lost in the operations. Sulfur may be dissolved iny caustic liquor to form some sodium suliid and some oxysulfur material, and such use of sulfur may be resorted to as to enhance the suliidity of the caustic liquor or/and as an aid in maintaining a desired ratio of NaOH to NazS fairly constant even when other conditions might tend to result in non-uniformity.

:It will thus be seen that the present invention presents improvements in the cooking of wood, etc., e. g. for the production of chemical pulp. in regenerative, cyclic or/and inter-related processes therefor, in the treatment of residual liquors, in the production of cooking liquors, and in individual steps of the process which involve the production of sodium carbonate from sodium sulfide by a novel carbonating treatment, and the production of a sodium acid carbonate by a regulated sulfiting of a corbonate of sodium.

Liquors obtained by dissolving sodium compounds, including sodium carbonate and sodium suliide, contained in the furnace product derived from residual liquor from a digesting operation employing cooking liquor supplied with a sulfurbearing compound of sodium, e. g. a sulilte, may vary considerably in proportions of the various constituents. In particular the ratio of sodium carbonate to sodium sulfide may vary throughout a fairly wide range. When the amount of sodium sulfide is relatively high, e. g. when the amount of sodium present as sodium sul'ilde is approximately as large as the amount of sodium present as sodium carbonate, it is somewhat more dimcult to treat the recovered sodium compounds to form a cooking liquor which contains the desired amount of a sulflte of sodium and little if any sodium thiosulfate, then it is when the amount of sodium carbonate in the furnace product is very much larger than the amount of sodium suldetherein. In the latter case there is more carbonate radicle available for providing the available carbon dioxide, e. g. upon the regulated sulting of a carbonate of sodium by means of SO2, to the sodium sulfide so as to form a volatile sulfide, e. g. as an acid carbonate of sodium, than when the amount of sodium sulfide in the furnace product is relatively high.

Therefore, there are some advantages in using a multiple-liquor mill, e. g. a two-liquors pulp mill so operated as to employ sulfur vin one instance primarily as a sulte and in another instance as a sulfide. For example, by cooking wood with an acid sulflte of sodium cooking liquor, either free from or with a suitable amount of sodium thiosulfate or/and sodium sulfate, to produce chemical pulp, separating resulting residual liquor from' resulting brous material, removing water from such liquor, furnacing resulting solids under strongly reducing conditions adapted to yield a furnace product which contains mostly sodium carbonate and sodium sulfide, with the latter being relatively high in amount, an advantage is obtained by causticizing the sodium carbonate and forming a cooking liquor which contains sodium hydroxide and a relatively large amount of sodium sulfide (and which cooking liquor may or may not contain some sodium sulte, or sodium thiosulfate, or both, in moderate amount), and employing such strongly alkaline cooking liquor to cook wood to produce chemical pulp and to form sodium-organic compounds including most of the sodium content of both the sodium hydroxide and the sodium sulfide, and to heatsolids derived from residual liquor resulting from such strongly alkaline cook to destroy organic matter and obtain a furnace product which contains most of its soda content in the form of sodium carbonate (and free from or with a relatively smaller 'or lesser amount of sodium sulfide) and then sulflting such sodium carbonate either without or after oxidizing or forming a volatile sulfld for the production of a sulfite of sodium and employing it in cooking liquor which is to have at the most only a small amount of sodium thiosulfate. Such an operation is` advantageous and especially desirable when the sulte of sodium cooking liquor so produced is to have a relatively large amount of SO2 over and above that required for forming normal sodium sulte (NazSOa) with the available soda. I

' The alkaline cooking liquor utilized in such a cycle preferably contains sodium hydroxide in greater amount than sodium sulnde and may also contain or be free from other chemicals in moderate amounts such as sodium sulte, sodium thiosulfate, sodium carbonate, sodium sulfate, etc.

In some instances, black liquor of the type described above resulting from a production of pulp material to produce pulp. Such direct suliiting of the black liquor may be carried out by dissolving S01 gas therein, or/and by adding sodium acid sulte thereto, advantageously adding enough SO2 so that the liquor is rendered acid to litmus and so that most of the precipltatible organic matter is precipitated; and such precipitated organic matter may be removed from the liquor in any suitable manner. The organic matter so removed may be furnaced advantageously along with solids derived from residual liquor resulting from a sulte of sodium type cooking operation. The organic matter thus returned furnishes carbonaceous matter to assist in carrying out a strongly reducing furnace treatment by which are Aproduced sodium carbonate and a relatively large amount of sodium sulfide. Any soda which is contained in the precipitated organic material may thus be added to the soda of residual liquor from a. sulte of sodium type of digestion operation. i

When all of such black liquor is thus subjected to a direct sulfiting treatment and the complete cycle is carried out in the" manner indicated, it will be seen that only one furnacing operation is employed although two cooking operations are carried out. This method therefore secures a more eilicient utilizationof sulfur and soda, since there is less danger of losing soda, or rather the amount lost may be reduced and some of the sulfur and soda constituents of the black liquor, which would ordinarily be lost during an additional fumacing treatment, are retained in the liquorwhen it is directly sulfited. The retained sulfur and soda in such case will be present in the sulte of sodium type of cooking liquor and become available for the production of sulfide-sulfur when a residual liquor resulting therefrom is furnaced under reducing conditions. When such direct sulilting of black liquor is practiced, the sulilte of sodium type of cooking liquorwill usually carry some thio compound, e. g. sodium thiosulfate, and therefore thesuliite of sodium type of cooking liquor should carry enough sulflte combined as sodium sulte to overcome the tendency of any such thio-compound or compounds to injure the fibres, e. g. by darkening them to a prohibitive degree, as previously pointed out. Thus liquors in which at least as much SO2 is present as normal sodium sulfite as is present asv sodium bisulilte may be produced in this manner vand employed to digest wood. The amount of thiomaterial therein will be in most, if not all, cases low enough for such liquors to be` satisfactorily used and satisfactorypulp be thereby obtained.

In case the operator does not choose to directly sultlte all of the black liquor as described in the preceding paragraphs, any desired portion of such black liquor may be chosen and directly suiflted. Any remaining portion of the black liquor may be treated to remove remaining water therefromv and the resulting solids furnaced under, e. g. reducing conditions to produce .sodium carbonate and sodium sulfid, the former usually being in preponderating amount. poundsmay be dissolved inwater and the re- Such sodium comassenso sulting solution causticized to form a sodium hydroxide-sodium sulilde cooking liquor of theen type previously referred to in this paragraph and such cooking liquor may be employed' to produce pulp. Instead oi causticizing such sodium carbonate-sodium sulildeliquor, a portion or all of it may be treated to produce a suliite of sodium type of cooking liquor and the latter employed to produce pulp. 'I'he black liquor, or'any desired portion oi' it, may be treated so as to furnace the solids thereof under either oxidizing or advantageously under reducing conditions, the latter being especially desirable when the sodium carbonate and sodium suliide in the furnace product are to be employed to produce a sodium hydroxidesodium suliide type o! cooking liquor; and such black liquor, or the desired portion thereof, may be treated separately or in conjunction with solids derived from residual liquor from the suliite of sodium type of cooking liquor, by subjecting the liquor witlry or without admixed solids to a strongly reducing treatment to form sodium carbonate and sodium suliide. Thus a cyclic process may be used in which black liquor may be directly suiiited to form a cooking liquor containing some SO: over and above the amount needed to form normal sodium suliite with the available soda, wood may be cooked therewith, the resulting residual liquor may be admixed with more black liquor and the admixture treated under suitable conditions to form sodium carbonate and sodium suliide; this sodium carbonate may be subjected to a causticizing step'and the resulting sodium lhydroxide and the sodium suli'lde may be employed to cook wood. etc. to produce pulp. In one respect, such a process may be considered as a means for supplying sodium` sulde to an alkaline cookingliquor by rst using the sulfur as a sulilte and later as a sulfide. and the amount of sulfur thus supplied' may be regulated so that the sodium suliide content oi' the alkaline cooking liquor can be kept fairly constant if desired. Sodium sultate,'or bisuifate, or both may be employed to replace soda lost in the operations; or sodium hydroxide or/and sodium carbonate may be employed for such purpose, the .hydroxide usually being supplied to the alkaline cooking liquor and the sodium carbonate Abeing advantageously employed toiorm a sulilte of sodium for the other type of cooking operation. In case it is desired to produce more pulp by the alkaline cooking liquor than usual and the sodium suliide content oi the alkaline cooking liquor becomes or tends to become too low for the best and most uniform results, elementary sulfur in right amount can be dissolved in the alkaline liquor before, during or after causticizing sodium carbonate, this procedure forming some sulde of sodium and some trioxy-suliur material such as sodium thiosulfate. 'I'he latter may be converted, atleast in part, into sodium suliite and sodium suliide by heating the solution of sodium hydroxide, sodium suliide and sodium thiosulfate under pressure to a high temperature for a sumcient period of time, e. g., heating up to around 180 to 200 degrees C. for a period of two or three hours, more or less, and apparently causing s'odium hydroxide to react with one of the sulfur atoms of the sodium thiosulfate to form sodium suliide and sodium sultlte.

'I'he processes of the present invention make feasible the cooking of short-iibred woods, such as poplars, gums, maples, birches, etc. by an advantageous acid suliite of sodium type of cooking liquor umier conditions adapted to produce a relatively high yield ot chemical pulp of good strength and n ing good bleaching qualities, and such cooking liquor may contain an amount of S: which provides a mixture of sodium sulilte and sodium bisulilte, with the former containing as much as or more SO2 than is contained in the bisulilte, i'or example, and care being taken to digest the wood to such a degree that it yields a chemical pulp oi! good bleaching qualities and which bleached pulp contains libres of ample strength and telting properties that -it can be employed in relatively large amount, for example, a preponderating amount, in the manufacture oi papers known as book papers and magazine papers, as well as writing papers, etc. Resinous pines which are generally considered unsuited to pulping by the conventional so-called acid suliite process employing calcium base, may be suitably pulped by the alkaline cooking liquor containing a preponderating amount oi' sodium hydroxide and a lesser amount of sodium sulde, such as described above. And when a moderate amount of sodium sulte is employed in such alkaline cooking liquor for digesting such resinous pine woods, the chemical pulp thus produced may be bleached to a i'alrly high white such that the bleached pulp containing the long libres, can be employed in admixture with the short iibredy bleached pulp produced by the special acid sulite type of cooking operation, to make the kinds of papers mentioned. This arrangement, which is just the opposite of that vwhich has heretofore been customarily employed (e. g. pulping spruce, etc. by the conventional acid-suliite process to produce the long iibred stock, and pulping the short-libred woods, such as poplar. by a sodium hydroxide cooking liquor, and employing these two pulps to produce such papers), is of especial utility in producing such papers from woods grown in the southern portions oi the United States, for example, since a number of the more readily available short-bred woods of such southern region do not usuali.; yield chemical pulps which are readily bleachable to a high white when cooked by the conventional soda process, and since the long-fibred woods, such as the pines, of such region are not ordinarily considered to be available for pulp-making purposes by the conventional acid sulfite process. By reversing the customary arrangement, i. e. pulping the shortflbred woods by means of a cooking liquor employing the sulfite radicle as an active digesting agent, e. g. as an acid sulte of sodium cooking liquor of suitable composition, and pulping the resinous woods by means of an alkaline liquor such as described above, book papers, magazine papers and writing papers of good quality can be readily obtained in an economical manner. 'I'he short-libred pulps obtained by such special acid suliite of sodium cooking liquors may be varied considerably by changing the ratio of combined SO2 to uncombined SO2 (e. g. NaaSOz to NaHSOa) and by varying the amount of chemicals, time and temperature of treatment, etc. Such pulps may be obtained so that they are suiiiciently hard to be suitable for writing-papers, or soft enough to be employed in large amount in the other types oi' papers, especially when the amount of normal sodium suliite is rather large as compared with the amount of sodium bisuliite. Such short-bred pulps are new and different pulps fromthose heretofore obtained from such woods by the conventional acid-sulflte-process and the papers made by the use, of, for ex- .f as pointed out.

The process or processes of the present invention are capable of numerous variations and modiflcations without departing from the spirit ot the invention.

In the claims the term black liquor is intended to include any residual liquor resulting from a digesting treatment of raw cellulosic-ilbrebearing material with a cooking liquor that contains a sodium compound as a digesting reagent.

1. A method of producing solid sodium bicarbonate anda solution containing sodium sulte and sodium bicarbonate which comprises treating a solution containing sodium suld with available carbon dioxide in amount not materially exceeding the amount required to convert sodium suld into carbonate of sodium, heating the solution to drive out the resulting hydrogen sulfid from the solution, cooling the solution to a temperature below 60 C., sullting the resulting solution with an amount oi' available sulfur dioxide not materially exceeding the amount required to convert all of the carbon dioxide of the carbonateof sodium into sodium bicarbonate, maintaining a concentration of the solution such lthat solid sodium bicarbonate is precipitated, and separating the resulting precipitated sodium bicarbonate from the sodium suliite solution.

2. The method of producing solid sodium bicarbonate and sodium sulte in solution which comprises treating a solution of sodium sulde at a temperature above 60 C. with solid sod'um bicarbonate in amount sufcient to release substantially all the sulfide-sulfur as hydrogen sulfide and to convert the sodium sulfide into sodium carbonate, removing the hydrogen sulde from the solution, cooling the resulting sodium carbonate solution to a temperature below 60 C., suliting the resulting cooled sodium carbonate solution until substantially all'the carbon dioxide is combined as sodium bicarbonate, said solution being suiciently concentrated so that a preponderating portion of the sodium bicarbonate is precipitated from the resulting solution `of sodium sulilte.

p 3. A method lof producing solld sodium bicarbonate and sodium sulflte in solution which comprises treating a solution containing sodium carbonate and sodium sulfide with solid sodium bicarbonate at a temperature in excess of 60 C., removing hydrogen sulfide from the hot solution, oxidizing the hydrogen sulde to produce sulfur dioxide, cooling the treated solution, sulting the solution at a temperature below 60 C., and during agitation thereof until substantially all the carbon dioxide is combined as sodium bicarbonate, and a preponderating portion oi' the sodium bicarbonate is precipitated, and separating precipitated sodium bicarbonate from the sodium sulte solution.

4. The method of producing sodium sulte in 4 solution and solid sodium bicarbonate which tion and the ratio of water to carbonate of sodium in the solution being so regulated that a preponderating portion of the resulting sodium bicarbonate separates out therefrom as solid sodium bicarbonate, and separating the solid sodium bicarbonate from the resulting solution.

5. The method of producing alkali sulflte and alkali bicarbonate which comprises subjecting a solution of alkali carbonate to a sulting treatment until substantially all the carbon dioxide of the alkali carbonate is combined as` alkali bicarbonate, and regulating the y.sulting treatment by maintaining the temperature of the solution below 60 C. and by agitating the solution while introducing available sulfur dioxide thereinto so as to substantially prevent the release of fre carbon dioxide from the solution. l

6. The method of obtaining a. sodium sulfite solution and solid sodium bicarbonate which comprises subjecting a solution containing sodium carbonate to a sulfting treatment at a temperature below 60 C. until substantially all of the carbon dioxide content of the sodium carbonate -is combined as sodium bicarbonate and some of the sodium bicarbonate is precipitated from the solution, and separating a solution of sodium sulte from the resulting solid sodium bicarbonate.

7. The cyclic process of converting sodium sulde into sodium suliite which comprises treating a solution of the sodium sulfide with sodium bicarbonate, removing from the solution hydrogen sulfide formed therein, burning the hydrogen sulfide to form `sulfur dioxide, cooling the solution to a temperature below.:60 C. treating the cooled solution with the sulfur dioxideso formed, the temperature of the solution being maintained low enough and th'e ratio of sodium bicarbonate to water being so regulated that solid sodium bicarbonate separates out from the solution separating solid sodium bicarbonate from the resulting sodium sulte solution, and utilizing the solid sodium bicarbonate for treating further amounts of sodium sulfide.

8. The Acyclic process of converting sodium sulfld into sodium sulte, which comprises treating a solutionbf the sodium suld with sodium bicarbonate, removing from the solution hydrogen suld formed therein by agitating the treated solution and maintaining it at a temperature above 60 C., cooling the solution to a temperature below 60 C. after hydrogen sulilde has been removed therefrom, vtreating the resulting cooled solution with sulfur dioxide to form sodium sulfte and sodium bicarbonate, and returning the sodium bicarbonate for treating further amounts of sodium sulfid in the further carrying out of the process.

9. The cyclic process of treating solutions containing sodium carbonate and sodium sulfid, which comprises adding sodium bicarbonate to such a solution, agitating the solution at a temperature in excess of 60 C. to form and remove hydrogen sulfid from the solution and to give a sodium carbonate solution containing the original sodium carbonate and that formed by the reaction between the sodium suld and sodium bicarbonate, cooling the sodium carbonate solution and maintaining it below 60 C. while treating such solution with sulfur dioxide to form sodium sulte and sodium bicarbonate, and returning the sodium bicarbonate for treating further amounts of a solution containing sodium carbonate and sodium suld.

l0. The process of producing sodium sulilte from sodium suliid which (a) treating the sodium sulde in alkaline solution with solid sodium bicarbonate in amount sumcient to decompose the sodium suliid thereof, thereby forming hydrogen sulild and sodium carbonate; (b) heating the solution to remove hydrogen suliid from the solution; (c) resulting from step (a) in the presenceof water, by means of available sulfur dioxide while the wateris maintained at a temperature below deg. C., thereby producing sodium suliite in solution and also producing sodium bicarbonate; (d) separating solid sodium bicarbonate from the solution referred to in step (c) and (e) treating sodium sulfid in step (a) with sodium bicarbonate produced in step (c).

l1. The process of treating residual liquor resulting` from a digesting treatment of raw cellulosic-nbre-bearing material with a liquor that contains normal sodium suliite and sodium carbonate, which comprises the following steps: (a) removing water from the residual liquor; (b) furnacing resulting carbonaceous matter and sodium-sulfur compounds under reducing conditions to produce sodium carbonate and sodium suld; (c) preparing an alkaline solution consodium carbonate and sodium sulnd thereby produced; (d) treating the alkaline solution with available carbon dioxide in amount at least as large as that which is chemically equivalent to the sodium sulfld therein, thereby converting sodium suliid thereof into a carbonate of sodium and producing hydrogen suld; (e) removing hydrogen suliid from the solution; (f) treating the solution while it is maintained at a temperature below 60 deg. C. with available sulfur dioxide, thereby obtaining sodium sulilte and sodium bicarbonate in the solution; and (g) digesting raw cellulosiciibre-bearing material by means of the solution resulting from step (f) 12. 'I'he process of treating residual liquor resulting from a digesting treatment of raw-cellulosic-nbre-bearing material with a liquor that contains a suliite of sodium, which comprises the,

following steps: (a) removing water from the residual liquor; (b) furnacing resulting carbonaceous matter and sodium-sulfur compounds derived therefrom under reducing conditions to produce sodium carbonate and sodium suliid; (c) preparing an alkaline solution containing sodium carbonate and sodium sulfld thereby pro-` duced; (d) treating the alkaline solution with solid sodium bicarbonate, produced by step (f), in amount suiiicient to convert` sodium sulnd thereof into a carbonate of sodium and form hydrogen suliid; (e) removing hydrogen suld from the solution and burning the hydrogen suld to form gaseous sulfur dioxide; (f) maintaining the solution, resulting from steps (d) and (e), at a temperature below 60 deg. C. and sulting it with gases that carry sulfur dioxide so as to obtain sodium sulflte and sodium bicarbonate in the solution and also obtain some solid sodium bicarbonate; (g) separating such solid sodium bicarbonate from sodium suliite and sodium bicarbonate contained in the solution; (h) treating such separated solid sodium bicarbonate with liquor as per step (d): and (i) suliiting the solution separated by step (a) with available sulfur dioxide so as to convert a carbonate of sodium thereof into a suliite of sodium for use in the further digestion of raw cellulosic-bre-bearing material.

13. The further improvement in the process of claim 12, characterized by the use of sulfur disuliiting sodium carbonate.

oxide formed by'step (e) for sulnting carbonate of sodium as per step (I) 14. The further improvement in the process of claim 12, characterized by the use of sulfur dioxide formed by step (e) for sulflting carbonate of sodium as per step (i).

l5. The further improvement in the process 0f claim l2, characterized by the step of introducing the residual liquor in finely divided condition into hot furnace gases produced by step (b) and subsequently introducing sodium-sulfur Ycompounds thereof into a furnace for the carrying out of step (b).

16. The further improvement in the process of claim 12, characterized by the step of recovering sulfur dioxide from gases produced by step (b) and forming a sultlte of sodium that contains such recovered sulfur dioxide, and employing such suliite of sodium in a cooking liquor for the digesting treatment therein referred to.

17. The further improvement in the process of claim 12, characterized by the step of passing relatively hot liquor resulting from step (e) countercurrent to a. relatively cool liquor that contains a sulflte of sodium in order to cool the former and to heat the latter by means of a heat exchanger.

18. The cyclic process of treating residual liquor resulting from a digesting treatment of raw cellulosic-flbre-bearing material with a cooking liquor that contains a sulte of sodium, which comprises the following steps: (a) evaporating water contained in the residual liquor; (b) furnacing resulting carbonaceous matter and sodium-sulfur compounds derived therefrom under reducing conditions to produce sodium carbonate and sodium sulfid and burning combustible matter also derived therefrom to produce furnace gases that contain sulfur dioxide; (c) preparing an alkaline solution containing sodium carbonate and sodium suld thereby produced; (d) treating the alkaline solution with available carbon dioxide to convert sodium suld thereof into carbonate of sodium and produce hydrogen sulfid; (e) removing hydrogen sulild from the solution; (f) treating furnace gases mentioned in means of liquor that contains a carbonate oi. sodium to recover sulfur 'dioxide therefrom land form a sulte of sodium; (g) including the recovered sulfur dioxide in contains a sulte of sodium and digesting raw cellulosic-iibre-bearing material therewith, thereby forming residual liquor; and repeating the process.

19. The further improvement in the process of claim 18, characterized by the utilization in step (f) of some carbonate of sodium in the solution resulting from the treatments set forth in steps (d) and (e).

20. In the process dened in claim 18, the further improvement which includes the following steps: (1) spraying the residual liquor into hot furnace gases formed by step (b), thereby evaporating water and recovering some sodium-sulfur compounds from the gases; (2) clarifying the sodium carbonate containing solution between steps (c) and (d) (3) burning the hydrogen suld removed by step (e) to form gaseous sulfur dioxide; (4) introducing sulfur dioxide thereby produced into a clarified sodium carbonate containing liquor subsequent to step (d) and step (e) to convert some of the sodium carbonate into sodium bicarbonate and some of it into sodium sulflte; (5) cooling the solution and separating solid sodium bicarbonate therefrom; and (6) using step (b) by a cooking liquor thatv auch separated solid sodium bicarbonate to decompose sodium sulnd as per step (d).

2l. In the art of treating residual liquor, resulting from a digesting treatment of raw-cellulosic-iibre-bearing material with aqueous cooking liquor that contains a suliite of sodium, in which art the water is evaporated and combustible organic matter thereof is burned to produce heat and sulfur and soda thereof are recovered and most of such recovered sulfur is used in forming a suiflte of sodium which is used in a subsequent similar digesting treatment, the improvement which comprises the following steps: (a) passing auch residual liquor through hot furnace gases produced in step (b), thereby evaporating water, cooling the gases. and recovering a portion only of the nrw-sulfur constituents carried by the (c) preparing an alkaline so-` lution that contains such recovered sodium carbonate and sodium sumd; (d) treating auch alkaline solution with solid sodium bicarbonate. produced in step (n) and separated in step (h) in amount sumcient to convert sodium suliid thereof into carbonate of sodium and form hydrogen sulfid; (e) removing hydrogen suind from the solution; (l) burning such hydrogen suld to gaseous sulfur dioxide; (a) sumting the solution, resulting from steps (d) and (e) while maintaining it at a temperature below 60 deg. C.. so as to produce sodium sulnte and sodium bicarbonate in the solution; (h) separating solid sodium bicarbonate from such dissolved sodium aulfite; (i) recovering sulfur dioxide `produced by step (f) and also sulfur dioxide carried by the furnace gases after step (d) has been carried out and combining suchrecovered sulfur dioxide with carbonate of sodium contained in liquor resulting from steps (d) and (e): and (i) employing such recovered sulfur dioxide in the form of a sulfite 0f sodium in cooking liquor for a digesting treatment of raw cellulosic-nbre-bearing material.

LINN BRADLEY.

EDWARD P. MCmFE. 25

' CERTIFICATE OF CORRECTION.

Prism No. 1,983, 189.

December Il, 1934.

LINN BRADLEY, Er' AL.

It is hereby certified that error appears in the printed-specification of the above numbered patent requiring correction as follows: Page 3, lsecond column, .line 45, for "cycle" read cyclic; page 4, first column, line 35, and second column, line 5, for "sulfite" read sulfide; page ll, first column, line 46, for "good" read wood; page 13, second column, line 7l, for "carbonate" read carbonate; page 16, firat column, line 38, claim 2, for "of" lrend containing; and page 17, first column, line 20. claim ll, for the syllable "car" read bicar; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in thePatent Office.

Signed and sealed this 19th day of March, A. D. i935.

(Sea l Leslie Frazer v Acting Conlniasioner of Patents.

auch separated solid sodium bicarbonate to decompose sodium sulnd as per step (d).

2l. In the art of treating residual liquor, resulting from a digesting treatment of raw-cellulosic-iibre-bearing material with aqueous cooking liquor that contains a suliite of sodium, in which art the water is evaporated and combustible organic matter thereof is burned to produce heat and sulfur and soda thereof are recovered and most of such recovered sulfur is used in forming a suiflte of sodium which is used in a subsequent similar digesting treatment, the improvement which comprises the following steps: (a) passing auch residual liquor through hot furnace gases produced in step (b), thereby evaporating water, cooling the gases. and recovering a portion only of the nrw-sulfur constituents carried by the (c) preparing an alkaline so-` lution that contains such recovered sodium carbonate and sodium sumd; (d) treating auch alkaline solution with solid sodium bicarbonate. produced in step (n) and separated in step (h) in amount sumcient to convert sodium suliid thereof into carbonate of sodium and form hydrogen sulfid; (e) removing hydrogen suind from the solution; (l) burning such hydrogen suld to gaseous sulfur dioxide; (a) sumting the solution, resulting from steps (d) and (e) while maintaining it at a temperature below 60 deg. C.. so as to produce sodium sulnte and sodium bicarbonate in the solution; (h) separating solid sodium bicarbonate from such dissolved sodium aulfite; (i) recovering sulfur dioxide `produced by step (f) and also sulfur dioxide carried by the furnace gases after step (d) has been carried out and combining suchrecovered sulfur dioxide with carbonate of sodium contained in liquor resulting from steps (d) and (e): and (i) employing such recovered sulfur dioxide in the form of a sulfite 0f sodium in cooking liquor for a digesting treatment of raw cellulosic-nbre-bearing material.

LINN BRADLEY.

EDWARD P. MCmFE. 25

' CERTIFICATE OF CORRECTION.

Prism No. 1,983, 189.

December Il, 1934.

LINN BRADLEY, Er' AL.

It is hereby certified that error appears in the printed-specification of the above numbered patent requiring correction as follows: Page 3, lsecond column, .line 45, for "cycle" read cyclic; page 4, first column, line 35, and second column, line 5, for "sulfite" read sulfide; page ll, first column, line 46, for "good" read wood; page 13, second column, line 7l, for "carbonate" read carbonate; page 16, firat column, line 38, claim 2, for "of" lrend containing; and page 17, first column, line 20. claim ll, for the syllable "car" read bicar; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in thePatent Office.

Signed and sealed this 19th day of March, A. D. i935.

(Sea l Leslie Frazer v Acting Conlniasioner of Patents. 

